Note: Descriptions are shown in the official language in which they were submitted.
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SCREENING DISK, ROLLER, AND ROLLER SCREEN FOR SCREENING
AN ORE FEED
FIELD OF THE INVENTION
This invention relates generally to screening of an ore feed using a roller
screen and more particularly to a screening disk and roller for use in a
roller
screen for screening an ore feed.
BACKGROUND OF THE INVENTION
Surface mining operations are generally employed to excavate an ore deposit
that is found near the surface of an ore body. Such ore deposits are usually
covered by an overburden of rock, soil, and/or plant matter, which may be
removed prior to commencing mining operations. The remaining ore deposit
may then be excavated and transported to a plant for processing to remove
commercially useful products. The ore deposit may comprise an oil sand
deposit from which hydrocarbon products may be extracted, for example.
In general, the excavated ore will include sized ore portions having a size
suitable for processing and oversize ore portions that are too large for
processing. Separation of the oversize ore portions from sized ore portions
may be performed by screening the excavated ore through a screen mesh
having openings sized to permit passage of sized ore portions through the
screen while preventing oversize ore portions from passing through the
screen. The oversize ore portions may be discarded and/or crushed to
produce sized ore. One problem associated with such screening is that the
screen mesh is prone to blockage.
Roller screens have also been used to screen ore. The roller screen has a
plurality of adjacently located rollers, each roller having a plurality of
screening
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disks mounted in spaced apart relation on a shaft. The screening disks
intermesh with screening disks on an adjacent roller of the roller screen to
define interstices for permitting passage of sized ore portions through the
roller screen. The rollers are coupled to a rotational drive to cause the
rollers
to rotate, thereby clearing blockages that may occur while screening the ore.
In the example of an oil sand ore deposit, such as the Northern Alberta oil
sands, the ore deposit comprises about 70 to about 90 percent by weight of
mineral solids including sand and clay, about 1 to about 10 percent by weight
of water, and a bitumen or oil film. The bitumen may be present in amounts
ranging from a trace amount up to as much as 20 percent by weight. Due to
the highly viscous nature of bitumen, when excavated some of the ore may
remain as clumps of oversize ore that requires sizing to produce a sized ore
feed suitable for processing. Due to the northerly geographic location of
many oil sands deposits, the ore may also be frozen making sizing of the ore
more difficult.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there is provided a screening
disk for use on a roller of a roller screen for screening an ore feed, the
roller
screen having a plurality of adjacently located rollers, each adjacently
located
roller having a plurality of screening disks mounted in spaced apart relation
on
a shaft, the mounted screening disks being operable to intermesh with
mounted screening disks on an adjacent roller of the roller screen to define
interstices between respective mounted screening disks for permitting
passage of sized ore portions through the roller screen. The screening disk
includes first and second opposing side working surfaces, and provisions for
mounting the screening disk on a shaft of the roller for rotation therewith.
At
least one of the first and second side working surfaces has a plurality of
protrusions operable to extend outwardly into an interstice between the at
least one side working surface and a side working surface of an adjacent
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mounted screening disk, the protrusions being operable to prevent oversize
portions of ore passing through the interstice between the intermeshing
screening disks. Each protrusion is removably secured to the screening disk to
facilitate replacement of the protrusion.
The protrusions each have a generally cylindrical shape.
Each protrusion of the plurality of protrusions may be dimensioned to provide
sufficient clearance distance between the protrusion and the side working
surface of the adjacent mounted screening disk to prevent contact between
the protrusion and the side working surface when operating the roller screen.
The interstice between the at least one side working surface and the side
working surface of the adjacent mounted screening disk may have a
dimension of about 60 millimeters and the clearance distance is in the range
of
about 10 millimeters.
Each protrusion may include a dowel pin operably configured to be received in
respective openings in at least one of the first and second side working
surfaces.
The protrusion and the dowel pin may be a unitary body.
The dowel pin may include a threaded portion operably configured to receive a
fastener extending through a portion of the screening disk for removably
securing the dowel pin in the opening.
The screening disk may include a third working surface extending between the
first and second side working surfaces, the third working surface being
operable to define an interstice between the third working surface and a shaft
of an adjacent roller when mounted in the roller screen, and the third working
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3A
surface may include at least one removable cap disposed circumferentially on
the screening disk, and the fastener received in the threaded portion of the
dowel pin extends through the removable cap and through the portion of the
screening disk and may be operable to secure the removable cap on the
screening disk.
The plurality of protrusions may be disposed in spaced apart relation on the
at
least one side working surface.
The plurality of protrusions may include a first plurality of protrusions
disposed
in spaced apart relation about a center of the at least one side working
surface.
The first plurality of protrusions may be disposed at a first radial distance
from
the center of the at least one side working surface and may further include a
second plurality of protrusions disposed in spaced apart relation about the
center of the at least one side working surface, the second plurality of
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protrusions being disposed at a second radial distance from the center of the
at least one side working surface.
Each of the first and second opposing side working surfaces may include
plurality of protrusions extending outwardly therefrom.
The screening disk may include a third working surface extending between
the first and second side working surfaces, the third working surface being
operable to define an interstice between the third working surface and a shaft
of an adjacent roller when mounted in the roller screen.
The third working surface may include at least one removable cap disposed
circumferentially on the screening disk.
The screening disk may include an opening bored through the screening disk
between the first and second opposing side working surfaces, the opening
being operable to receive a first fastener having a first threaded portion
operable to receive a threaded portion of a second fastener for securing the
at
least one removable cap to the screening disk.
The provisions for mounting the screening disk on a shaft may include a
centrally located opening extending between the first and second opposing
side working surfaces of the screening disk, the opening being operably
configured to permit the screening disk to be received on the shaft and to
engage the shaft for rotation therewith.
In accordance with another aspect of the invention there is provided a roller
for use in a roller screen for screening an ore feed. The roller includes a
shaft, and a plurality of screening disks mounted in spaced apart relation on
the shaft. The screening disks are operable to intermesh with mounted
screening disks on an adjacent roller of the roller screen to define
interstices
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between respective mounted screening disks for permitting passage of sized ore
portions through the roller screen. At least one of the plurality of screening
disks
on the shaft includes a screening disk as claimed above.
In accordance with another aspect of the invention there is provided a roller
screen for screening an ore feed. The roller screen includes a plurality of
adjacently located rollers. Each roller includes a shaft having a plurality of
screening disks mounted in spaced apart relation on the shaft the mounted
screening disks being operable to intermesh with mounted screening disks on an
adjacent roller of the roller screen to define interstices between respective
mounted screening disks for permitting passage of sized ore portions through
the
roller screen. At least one of the screening disks on at least one of the
rollers
includes a screening disk as claimed above.
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Each of the screening disks on the at least one roller may include a
protrusion
extending outwardly from each of the first and the second side working
surfaces
and an adjacent roller to the at least one of the adjacently located rollers
may
include a plurality of screening disks that do not include protrusions.
Each screening disk may include a third working surface extending between the
first and second side working surfaces, one interstice of the plurality of
interstices
being defined extending outwardly from a shaft of an adjacently located roller
toward the third working surface, and the roller screen may further include at
least one spacer disposed in the one interstice for confining an extent of the
one
interstice to a region disposed generally between the third working surface
and
the shaft, the at least one spacer being operable to prevent oversize ore
portions
from passing through the one interstice.
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The at least one spacer may include an annular spacer disposed in the one
interstice.
The annular spacer may be supported on the shaft and disposed adjacent to one
of the side working surfaces of the screening disk.
The annular spacer may be connected to one of the side working surfaces of the
screening disk and extends outwardly therefrom into the one interstice.
The at least one annular spacer may include a first annular spacer disposed
adjacent to the first side working surface of a first screening disk, and a
second
annular spacer disposed adjacent to the second side working surface of a
second screening disk located on the shaft adjacent to the first screening
disk.
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Each screening disk may include a third working surface extending between the
first and second side working surfaces, one interstice of the plurality of
interstices
being defined extending outwardly from a shaft of an adjacently located roller
toward the third working surface, and may further include provisions for
restricting an extent of the one interstice to a region disposed generally
between
the third working surface and the shaft, the provisions for restricting being
operable to prevent oversize ore portions from passing through the one
interstice.
The screening disk may include a generally cylindrical body portion having
first
and second opposing side working surfaces, provisions for engaging the shaft
for
rotation therewith, and a third working surface extending across the screening
disk between the first and second side working surfaces, the third working
surface having a plurality of teeth, each tooth having a tooth face and a
tooth
back, the tooth back extending between adjacent tooth faces of the plurality
of
teeth and the tooth face being operably configured to fragment the ore feed to
produce ore portions that are sized for passage through the interstices, the
tooth
face having wear resistant working surface.
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The wear resistant working surface on the tooth face may include a wear
resistant overlay selectively applied to the tooth face.
The wear resistant overlay material may include one of tungsten carbide and
chromium carbide.
Other aspects and features of the present invention will become apparent to
those ordinarily skilled in the art upon review of the following description
of
specific embodiments of the invention in conjunction with the accompanying
figures.
The roller screen may include a centrally located opening extending between
the first and second opposing side working surfaces for engaging the shaft
and at least one keyway formed in the opening, the keyway being operably
configured to receive a key for coupling the body of the screening disk to the
shaft for rotation therewith.
The opening may include a hub for engaging the shaft and the keyway may
include a keyway recess formed in the hub.
The key and respective keyways may be toleranced to provide a loose sliding
fit between the surfaces of the key and the keyway to prevent ingress of
abrasive materials.
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BRIEF DESCRIPTION OF THE DRAWINGS
In drawings which illustrate embodiments of the invention,
Figure 1 is a perspective view of a roller screen in accordance with a
first
embodiment of the invention;
Figure 2 is a cross sectional view of a portion of the roller screen shown
in
Figure 1 taken along the line 2-2;
Figure 3 is a perspective view of a screening disk used in the roller
screen
shown in Figure 1;
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Figure 4 is a perspective view of a screening disk in accordance with an
alternative embodiment of the invention;
Figure 5 is a cross sectional view of a portion of a roller screen
incorporating
the screening disk shown in Figure 4;
Figure 6 is a top view of a portion of a roller screen including a
screening disk
in accordance with another embodiment of the invention;
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Figure 7 is a perspective view of a screening disk in accordance
with yet
another embodiment of the invention;
Figure 8 is a perspective exploded view of a screening disk in
accordance
with a further embodiment of the invention;
Figure 9 is a cross sectional view of a portion of the screening
disk shown
in Figure 8 taken along the line 9-9;
Figure 10 is a perspective view of a removable cap in accordance with
another alternative embodiment of the invention;
Figure 11 is a perspective view of a removable cap in accordance
with
further alternative embodiment of the invention; and
Figure 12 is a perspective view of a removable cap in accordance
with yet
another embodiment of the invention.
DETAILED DESCRIPTION
Referring to Figure 1, a roller screen for screening an ore feed is shown
generally at 100. The roller screen 100 includes first and second sidewalls
124 and 126 and an end wall 132, located at a first end of the roller screen
100. The end wall 132 extends between the sidewalls 124 and 126. The
roller screen 100 also includes a discharge ramp 138 located at a second end
of the roller screen 100. The discharge ramp 138 also extends between the
first and second sidewalls 124 and 126.
The roller screen 100 further includes a plurality of adjacently located
rollers
102. In the embodiment shown the roller screen 100 includes eight rollers
104 to 118, but other embodiments may include additional rollers or fewer
rollers than shown in Figure 1. Each roller includes a shaft 122 which is
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mounted for rotation in bearings 128 and 129, the bearings being located in
the respective sidewalls 124 and 126. In one embodiment the bearing may
comprise a labyrinth seal to prevent ingress of contaminants, which may
cause premature failure of the bearings. In Figure 1, two of the screening
disks on the roller 118 have been omitted to reveal the shaft 122 and the
bearing 129. Similarly, two of the screening disks on the roller 104 have been
omitted to reveal the shaft 122.
The roller screen 100 further includes a drive motor 130 associated with each
of the rollers 102 for supplying a rotational torque to the respective shafts
122
of the roller. In the embodiment shown in Figure 1, each roller 102 has an
associated drive motor 130, but in other embodiments a single drive motor
may be coupled more than one roller for providing a drive torque to more than
one roller.
Each roller 102 further includes a plurality of screening disks 120 mounted in
spaced apart relation on the shaft 122. The mounted screening disks 120
intermesh with mounted screening disks on an adjacent roller. For example,
the mounted screening disks 120 on the roller 104 intermesh with mounted
screening disks on the adjacent roller 106. The end wall 132 also includes a
plurality of static plates 134, which extend outwardly from the end wall and
intermesh with the screening disks 120. The intermeshing screening disks
120 and static plates 134 define a plurality of interstices therebetween for
permitting passage of sized ore portions through the roller screen 100. In
general, the spacing between screening disks 120 defines dimensions of the
interstices, which in turn determines a passing size for the roller screen
100.
In one embodiment where an oil sand ore feed is to be processed, the desired
passing size is about 60 mm by about 60 mm by about 100 mm. In other
embodiments the passing size may be larger or smaller on one or more
dimensions.
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in the embodiment shown, each screening disk 120 includes plurality of
protrusions 140 extending outwardly from a side working surface 184 of the
screening disk. Portions of the rollers 116 and 118 of the roller screen 100
are shown in sectional view in Figure 2 at 160. Referring to Figure 2, the
intermeshing disks 120 define interstices 162 (shown in broken outline)
including an interstice 164 between the screening disk 120 and the shaft 122,
and an interstice 166 between adjacent screening disks. The protrusion 140
effectively divides the interstice 166 into two smaller interstices, thereby
preventing elongate oversize portions of ore from passing through the
interstice. Similarly, the plurality of static plates 134 further define
interstices
168 and 170 between the static plates 134 and the screening disks 120, and a
respective protrusion 140 divides the interstice 170 into two smaller
interstices.
In operation, an ore feed including some sized ore portions and some
oversize ore portions, is received at an input end 136 of the roller screen
100.
The sized ore portions have passing size dimensions that should permit
passage through the interstices 160, while the oversize ore portions have at
least one dimension too large to permit passage through the interstices. In
one operational embodiment, each of the rollers 102 are rotated in a direction
shown by the arrow 142 to cause the ore feed to be transported along the
roller screen from the input end 136 to the discharge ramp 138. While the ore
feed is being transported, sized ore portions are able to pass through the
interstices 160 and fall through the roller screen 100. In general the roller
screen is disposed over a container (not shown) that receives the sized ore
portions for further processing. Oversize ore portions are generally prevented
from passing through the interstices 160, unless in the process of being
transported, the action of the screening disks 120 causes the oversize ore
portions to be fragmented into sized ore portions. In general, the screening
rollers 102 of the roller screen 100 provide some sizing action resulting in
fragmentation of some oversize ore portions into ore portions of passing size.
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Oversize ore portions that reach the discharge ramp 138 are discharged from
the roller screen 100 and may be further sized in a separate process or may
be discarded. Alternatively, as disclosed in Canadian Patent application
CA2640514 filed on October 7, 2008 and entitled "Method and Apparatus for
Processing an Ore Feed", additional opposing sizing rollers may be included
to cause the oversize ore portions in the ore feed to be sized while being
transported along the roller screen.
The screening disk 120 is shown in greater detail in Figure 3. Referring to
Figure 3, the screening disk 120 includes a body portion 180 having a
centrally located opening 182 for mounting the screening disk on the shaft
122 (shown in Figure 1). In the embodiment shown, the centrally located
opening 182 is defined by a mounting hub 188, which may be welded to the
body portion 180. The body portion 180 defines a first side working surface
184. A second side working surface (not shown in Figure 3) is defined on an
opposite side of the body portion 180. The screening disk 120 further
includes a third working surface 186 extending between the first and second
side working surfaces.
In the embodiment shown in Figure 3, the protrusions 140 have a truncated
conical shape. In other embodiments the protrusions may have a cylindrical
shaped or a generally cubic shape (as shown in Figure 7). The protrusions
140 are disposed in uniform spaced apart relation about a center of the first
side working surface 194, each protrusion being spaced a distance R from the
center of the first side working surface 184. Referring back to Figure 2, the
protrusions 140 are dimensioned to provide an operational clearance distance
D between an extent 172 of the protrusion 140 and the adjacent screening
disk. In general the clearance D is selected to provide sufficient clearance
to
prevent contact between the extent 172 and a side working surface of the
adjacent screening disk, during operation of the roller screen 100. In one
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embodiment a width W of the screening disk 120 may be about 75 mm, the
distance between side working surfaces of adjacent screening disks may be
about 50 mm or between about 50 mm and about 60 mm, and the clearance
distance D may be about 10 mm or more. In other embodiments the distance
between side working surfaces of adjacent screening disks may be larger.
For example, in another embodiment, the distance between side working
surfaces may be about 60 mm to about 100 mm to provide yet further spacing
when working with suitable feed material or when the feed material will be
further processed downstream with a further or secondary sizer. In yet
another embodiment, the distance between side working surfaces may be
greater than 100 mm to provide yet further spacing. For instance, in yet
another embodiment, the distance between side working surfaces may be
about 100 mm to about 150 mm.
Referring now to Figure 4, a screening disk in accordance with an alternative
embodiment of the invention is shown generally at 200. The screening disk
200 includes a body portion 202, defining a first side working surface 204.
The screening disk 200 includes a first plurality of protrusions 206, which
are
spaced apart about a center of the first side working surface 204. Each of the
first plurality of protrusions 206 are located a distance R1 from the center
of
the side working surface 204. The screening disk 200 further includes a
second plurality of protrusions 208, which are spaced apart about a center of
the first side working surface 204. Each of the second plurality of
protrusions
206 are located a distance R2 from the center of the side working surface 204.
In this embodiment the first plurality of protrusions 206 are also angularly
offset from the second plurality of protrusions 208 by an angle 0. However, in
other embodiments members of each of the first and second plurality of
protrusions may be radially aligned (i.e. cl) = 0 degrees). The screening disk
200 further includes a third working surface 214 extending between the first
and second side working surfaces.
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Still referring to Figure 4, the screening disk 120 also includes a mounting
hub
210, which may welded to the body portion 202 for example. The mounting
hub 210 includes a spacer portion 212, which extends outwardly from the first
side working surface 204. Accordingly, in this embodiment the spacer portion
212 has a generally annular shape.
A portion of a roller screen having screening disks in accordance with the
embodiment shown in Figure 4 is shown generally in Figure 5 at 230.
Referring to Figure 5, the first and second plurality of protrusions 206 and
208
on the intermeshing screening disks 200, and the spacer portions 212 define
a plurality of interstices 232 between adjacent screening disks. The
interstices 232 include a first interstice 234, which is confined in extent by
the
spacers 212 to a region between the third working surface 214 and the shaft
122. Advantageously, the spacers 212 prevent oversize ore portions from
passing through the first interstice 234. The interstices 232 further include,
a
second interstice 236 between the spacer 212 and the protrusion 206, a third
interstice 238 between the protrusions 206 and 208, and a fourth interstice
240 between the protrusion 208 and the spacer 212 located on the shaft 122
of the adjacent roller 118. Advantageously, the radii R1 and R2 are selected
to
cause the second, third, and fourth interstices 234, 236, and 238 to prevent
oversize ore portions from passing through the respective interstices, while
passing ore portions of passing size.
Various other configurations of protrusions and spacers are possible. For
example, as shown in top view in Figure 6, a screening disk 250 has a first
side working surface 252 and a second side working surface 254. The
screening disk 250 includes protrusions 256 located on the first side working
surface 252 at a radius R2 from the center and protrusions 258 located on the
second side working surface 254 at a radius R1 from the center. Referring
back to Figure 1, in other embodiments screening disks on alternating rollers
(for example the rollers 104, 108, 112, and 106) may include protrusions
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located on each of the first and second side working surfaces while the
remaining rollers (i.e. rollers 106, 110, 114, and 118) may not include
protrusions.
An alternative embodiment of a spacer 260 is also shown in Figure 6. The
spacer 260 has a generally cylindrical shape with an internal bore (not shown)
sized to be received on a shaft 264 between the spaced apart screening disks
250. The spacer 260 includes a centrally located recess 262. When
assembled on a roller, the spacer 26 is disposed in-between adjacent
screening disks 250 and is operable to confine an extent of an interstitial
region between a third working surface 266 of the screening disk 250 and the
shaft 264, as described above in connection with Figure 5.
Referring back to Figure 4 in the embodiment shown, the hub 210 of the
screening disk 200 includes a keyway recess 216 for receiving a key for
coupling the screening disk 200 to the shaft 122. Referring to Figure 7, the
screening disk 200 is shown mounted on a shaft 284, which includes a
keyway recess 282 corresponding to the keyway recess 216 on the hub 210.
When mounting the screening disk 200 on the shaft 122, the corresponding
keyway recesses 216 and 282 are aligned and a key 280 is inserted into the
keyway. Advantageously, the key 280 and keyway recesses 216 and 282 are
toleranced to provide a loose sliding fit between the surfaces of the key and
the keyway to prevent ingress of sand or other abrasive materials, which
could cause failure of the coupling, between the disk 200 and the shaft 284.
In the embodiment shown in Figure 7, the screening disk 200 has protrusions
286 having a generally cubic shape in place of the truncated conical shaped
protrusions shown in other embodiments.
Referring now to Figure 8, an alternative embodiment of a screening disk for
use in the roller screen 100 is shown generally at 300. The screening disk
300 includes first and second separable body portions 302 and 304. The first
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body portion 302 includes a first mounting hub portion 306 attached to the
first
body portion and the second body portion 304 includes a second mounting
hub portion 308 attached to the second body portion and 304. Together, the
first and second mounting hub portions 306 and 308 define an opening 310
having at least one planar portion 312 for engaging a corresponding planar
portion of a shaft (not shown). In the embodiment shown in Figure 8, the
opening 310 has a generally square opening for mounting on a shaft having a
corresponding square cross section.
The body portions 302 and 304 together form first and second opposing side
working surfaces 316 and 318. A third working surface 320 is provided by a
removable cap 314 extending across the screening disk between the first and
second side working surfaces 316 and 318. In the embodiment shown, four
such removable caps are provided to define a third working surface extending
around a circumference of the screening disk 300.
The removable cap 314 has a first end 322 and a second end 324. The first
end 322 includes a through opening 326 for receiving a first fastener 330.
The second body portion 304 also includes an opening 328, which is aligned
with the opening 326 for receiving the first fastener 330 for securing the
first
end of the removable cap 314 to the second body portion 304. Similarly, the
second end 324 includes a through opening for receiving a second fastener
332 for securing the second end of the removable cap 314 to the first body
portion 302. In the embodiment shown, further openings are provided in the
removable cap 314 for receiving further fasteners 334 for securing the cap to
the first and second body portions. The removable cap 314 further includes a
protruding channel portion 338 for engaging corresponding channel portions
340 in the body portions 302 and 304. In other embodiments, the protruding
channel may be provided on the body portions 304 and 304, and the
removable cap 314 may include a corresponding channel for receiving the
protruding channel portion.
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When mounting the screening disk 300, the first and second body portions
302 and 304 are separately mounted on the shaft and the respective first and
second ends 322 and 324 of the removable cap 314 are secured to the
respective first and second body portions 302 and 304. Similarly, the first
and
second ends of an oppositely located removable cap 336 are secured to the
respective first and second body portions 302 and 304, thereby securing the
screening disk 300 on the shaft. The channel portion 338 acts to locate the
cap 314 on the body portion and to prevent lateral movement of the cap
during operation of the roller screen.
Referring to Figure 9, the removable cap 314 and a portion of the second
body portion 304 of the screening disk 300 is shown in cross section at 360.
The channel portion 338 of the removable cap 314 is shown located in the
corresponding channel portion 340 of the second body portion 304. The
second body portion 304 further includes a through opening 362, extending
through the body portion between the first and second working surfaces 316
and 318. The opening 328 extends between the channel portion 340 and the
through opening 362. The through opening 362 is dimensioned to receive a
dowel pin 364. The dowel pin 364 has a threaded portion 366 for receiving a
threaded portion of the fastener 330 for securing the cap 314 to the second
body portion. Advantageously, should the dowel pin 364 require replacement,
it is a relatively simple matter to drive out a damaged dowel pin 364 and
insert
a replacement. Referring back to Figure 8, in the embodiment shown each
dowel pin 364 includes a protrusion 342, the dowel pin and protrusion forming
a unitary body. In other embodiments the protrusions may be welded or
otherwise attached to the sides of the screening disk.
Advantageously, the screening disk 300 facilitates replacement of a damaged
or worn screening disk on a roller in-situ, since the damaged disk may be
removed without removing the roller from the roller screen 100. The rollers
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are extremely heavy and require specialized rigging equipment for removal, to
permit access to the shaft, and thus in-situ disk replacement represents a
substantial serviceability improvement. The removable protrusions 342 further
permit replacement of worm protrusions on a screening disk.
Referring now to Figure 10, a removable cap in accordance with an
alternative embodiment is shown generally at 400. The removable cap 400
includes a transverse keyway 402 in channel portion 338 for receiving a key
404 for transmitting a torque from the body portion of the screening disk to
the
cap. In this embodiment, the screening disk has a corresponding transverse
keyway (not shown). Advantageously, by transmitting a substantial portion of
the torque through the key 404, the fasteners 330, 332, and 334 shown in
Figure 8 are subjected to reduced shearing stress thereby preventing
potential failure of the fasteners. In other embodiments, the key 404 may be
integrally formed in the replaceable cap 400.
Referring to Figure 12, a removable cap according to yet anther embodiment
is shown generally at 450. The removable cap 450 in this embodiment
includes three hook-shaped teeth 452 for gripping ore portions while
screening the ore feed. The teeth 452 may be included to facilitate some
sizing action for reducing the size of oversize ore portions in the ore feed.
Advantageously, removable caps with a variety of different shaped teeth may
be fabricated to permit configuration of the screening disks for screening of
a
particular ore feed. The removable cap 450 also differs from the removable
cap 314 in that the protruding channel portion 338 has been omitted in favor
of a circumferential key 454, which is received in a channel 456 in the cap
and
engages the corresponding channel portion 340 (shown in Figure 8).
The removable cap 400 may be fabricated by a casting process, and in one
embodiment may be cast from white iron. Cast white iron is extremely
hardwearing and is preferably cast into a final shape, since machining is
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generally limited to grinding operations.
In embodiments where the
removable cap 400 is fabricated from cast white iron, tolerances of the
screening disk receiving the cap should take into account the variability of
the
casting process. The inventors have further found that when the width W of
the disk (as defined in Figure 2) is too small, the required size of the
fasteners
330, 332, and 334 (shown in Figure 8) causes the cap 400 to be prone to
cracking. Accordingly, Applicant has determined that white iron castings, the
cap width W should preferably be greater than about 75 mm.
Advantageously, when the cap 400 is cast from white iron, the entire cap is
extremely wear resistant due to the distributed chromium carbides in the bulk
material of the cap.
Referring to Figure 11, a removable cap in accordance with another
embodiment of the invention is shown generally at 430. In this embodiment,
the removable cap 430 has a different working surface 432 to the cap 400
shown in Figure 10. Specifically the working surface 432 comprises a plurality
of teeth (434 to 438), each tooth having a tooth face 440, and a tooth back
442. The tooth face 440 is defined by an intended direction of rotation of the
cap 430 when in operation. In this embodiment, the cap 430 is fabricated
from a material having ordinary wear characteristics, and the cap is post
treated to provide a wear resistant working surface 432. In one embodiment,
a tungsten-carbide overlay is applied to the cap using a plasma transfer arc
process. Advantageously, due to the high cost of providing a tungsten-
carbide overlay, the overlay may be selectively applied to the tooth face 440
as shown by the shaded areas in Figure 11. In this case the tooth back 442
remains un-hardened. Generally during operation, a majority of the wear
occurs on the tooth face 440 and wear of the tooth back 442 is not
significant.
In one embodiment the thickness of the selectively applied tungsten-carbide
layer is about 5 mm. In other embodiments, the wear resistant overlay may
comprise chromium carbide.
CA 02673865 2009-07-24
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Although specific embodiments of the invention have been described and
illustrated, such embodiments should be considered illustrative of the
invention only and not as limiting the invention as construed in accordance
with the accompanying claims. Various modifications of form, arrangement of
components, steps, details and order of operations of the embodiments
illustrated, as well as other embodiments of the invention, will be apparent
to
persons skilled in the art upon reference to this description. It is therefore
contemplated that the appended claims will cover such modifications and
embodiments as fall within the true scope of the invention. In the
specification
including the claims, numeric ranges are inclusive of the numbers defining the
range. Citation of references herein shall not be construed as an admission
that such references are prior art to the present invention.
